Synchronization after restart of a fc switch

ABSTRACT

Examples of the present disclosure provide a method and an apparatus for synchronization after restart of a FC switch. For example, when a FC switch which is restarted detects that a neighbor FC switch has already established an adjacency relationship with the restarted FC switch, the adjacency relationship between the restarted FC switch and the neighbor FC switch is maintained, and the neighbor FC switch is requested to perform LSR initial synchronization to the restarted FC switch under a circumstance that the adjacency relationship is kept.

BACKGROUND

Fabric Shortest Path First (FSPF) protocol is a link-based dynamicrouting discovery protocol and is used in a Fiber Channel (FC) network.Each FC switch supporting the FSPF protocol can use a Link State Record(LSR) generated by the FC switch itself to describe a relationshipbetween the FC switch and a neighbor FC switch. The FC switch and theneighbor FC switch mutually synchronize the LSR through a Link StateUpdate (LSU) packet and a Link State Acknowledgement (LSA) packet of aSwitch Fabric Internal Link Service (SW_ILS) protocol, so that each FCswitch can detect the topology of the FC network through therelationship described by the LSR, and then routing is achieved based onthe detected topology.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present disclosure are illustrated by way of example andnot limited in the following figure(s), in which like numerals indicatelike elements, in which:

FIG. 1 is a flowchart illustrating a method for synchronization afterrestart of a FC switch according to an example of the presentdisclosure.

FIG. 2 is a flowchart illustrating a method for synchronization afterrestart of a FC switch according to another example of the presentdisclosure.

FIG. 3 is a schematic diagram illustrating a neighbor state machineaccording to an example of the present disclosure.

FIG. 4 is a flowchart illustrating an example of a method forsynchronization after restart of a FC switch according to an example ofthe present disclosure.

FIG. 5 is a schematic diagram illustrating a hardware structureaccording to an example of the present disclosure.

FIG. 6A is a schematic diagram illustrating a hardware structure of anapparatus for synchronization after restart of a FC switch according toan example of the present disclosure.

FIG. 6B is a schematic diagram illustrating a hardware structure of anapparatus for synchronization after restart of a FC switch according toan example of the present disclosure.

FIG. 7A is a schematic diagram illustrating a hardware structure ofanother apparatus for synchronization after restart of a FC switchaccording to an example of the present disclosure.

FIG. 7B is a schematic diagram illustrating a hardware structure ofanother apparatus for synchronization after restart of a FC switchaccording to an example of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, the present disclosure will be described in further detailwith reference to the accompanying drawings and examples.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure. Itwill be readily apparent however, that the present disclosure may bepracticed without limitation to these specific details. In otherinstances, some methods and structures have not been described in detailso as not to unnecessarily obscure the present disclosure. As usedherein, the term “includes” means includes but not limited to, and theterm “including” means including but not limited to. The term “based on”means based at least in part on. In addition, the terms “a” and “an” areintended to denote at least one of a particular element.

Generally, after a FC switch and a neighbor FC of the FC switch discovereach other, LSR initial synchronization may be performed, and all LSRsin a Link-State Database (LSDB) of the other side are synchronized to alocal LSDB during the process of the initial synchronization.

After the FC switch and the neighbor FC switch complete the initialsynchronization, an adjacency relationship is established between thetwo FC switches. Each of the two FC switches may calculate the shortestrouting from local to any one of other FC switches based on thesynchronized LSR in the local LSDB, so that each FC switch can achievethe routing forwarding of the FSPF protocol through a neighbor FC switchwhich establishes the adjacency relationship with the FC switch.

After the FC switch and the neighbor FC switch establish the adjacencyrelationship between each other, if the network topology is changed, thetwo FC switches may perform topology updating synchronization under thecircumstance that the adjacency relationship is kept, and mutuallysynchronize respective LSRs relating to the topology change during theprocess of the topology updating synchronization; after the FC switchand the neighbor FC switch establish the adjacency relationship betweeneach other, if a corresponding port of one of the FC switches is pulledout or the FC switch is restarted, the FC switch re-initiates a neighbordiscovery process between the FC switch and the neighbor FC switch, sothat the established adjacency relationship between the two FC switchesis deleted, and a new adjacency relationship is re-established after there-initiated neighbor discovery and the initial synchronization iscompleted.

The above working principles of the FC switch leads to changes of therouting in the FC network due to the restart of the FC switch; however,in some circumstances, it is necessary to ensure that the routing doesnot change after the restart of the FC switch.

Generally, routing associated with a restarted FC switch in a FC networkincludes two parts as follows: one part is routing from another FCswitch in the FC network to the restarted FC switch; and another part isrouting from the restarted FC switch to the other FC switch in the FCnetwork.

Therefore, in order to ensure that the routing associated with therestarted FC switch in the FC network is not changed before and afterthe restart of the restarted FC switch, examples of the presentdisclosure employ different approaches for processing the above twoparts of routing.

Firstly, in order to ensure that the routing from the other FC switch inthe FC network to the restarted FC switch is not changed before andafter the restart of the restarted FC switch:

the restarted FC switch determines, within a predetermined waitingperiod after the restart, whether there is a neighbor FC switch whichhas already established an adjacency relationship with the restarted FCswitch before the restart of the restarted FC switch rather thanimmediately re-initiates a neighbor discovery process with a neighbor FCswitch;

if it is determined that there is not the neighbor FC switch which hasalready established the adjacency relationship with the restarted FCswitch before the restart of the restarted FC switch, the neighbordiscovery process with the neighbor FC switch is re-initiated;

if it is determined that there is the neighbor FC switch which hasalready established the adjacency relationship with the restarted FCswitch before the restart of the restarted FC switch, the neighbordiscovery process with the neighbor FC switch is not re-initiated, theadjacency relationship between the restarted FC switch and the neighborFC switch is maintained immediately, and the neighbor FC switch isrequested to perform LSR initial synchronization to the restarted FCswitch under a circumstance that the adjacency relationship is kept.

In this way, state rollback occurring in the neighbor FC switch can beavoided and deletion of the adjacency relationship between the neighborFC switch and the restarted FC switch can be avoided. Therefore, therouting from the other FC switch in the FC network to the restarted FCswitch through the neighbor FC switch being deleted can be avoided, sothat the routing from the other FC switch in the FC network to therestarted FC switch is not changed before and after the restart of therestarted FC switch.

Secondly, in order to ensure that the routing from the restarted FCswitch to the other FC switch in the FC network is not changed beforeand after the restart of the restarted FC switch:

as LSRs in the restarted FC switch before the restart are the same withLSRs in the neighbor FC switch, and the LSRs in the neighbor FC switchwhere the state rollback does not occur is not changed, the restarted FCswitch is able to detect the same LSRs as ones before the restart of therestarted FC switch through the initial synchronization with theneighbor FC switch which has already established the adjacencyrelationship with the restarted FC switch.

In this way, the routing from the restarted FC switch to the other FCswitch in the FC network which is re-calculated by the restarted FCswitch is the same as one before the restart of the restarted FC switch;moreover, the restarted FC switch triggers routing calculation after theinitial synchronization with the neighbor FC switch which has alreadyestablished the adjacency relationship with the restarted FC switch iscompleted rather than performs the routing calculation during theprocess of the initial synchronization. Therefore, frequent changing ofthe routing from the restarted FC switch to the other FC switch in theFC network which is re-calculated by the restarted FC switch followingthe process of the initial synchronization can be avoided. In this way,a change in the routing in the FC network due to the restart of the FCswitch can be avoided.

The restart described in examples of the present disclosure can be notonly the restart triggered by a master-backup switch in a FC switch witha distributed structure, but also the restart resulting from a varietyof reasons such as a restart occurring in a FSPF protocol layer, and arestart initiated by a FC switch for re-synchronizing (e.g., the totalchecksum of a local LSDB is inconsistent with the checksum of all LSRs).Based on the above principles, an example of the present disclosureproposes a method for synchronization after restart of a FC switch.

FIG. 1 is a flowchart illustrating a method for synchronization afterrestart of a FC switch according to an example of the presentdisclosure. As shown in FIG. 1, when the FC switch is restarted, themethod is performed by the restarted FC switch. The process of themethod includes operations as follows.

In block 101, when the FC switch is restarted, and when a packet forkeeping alive an adjacency relationship, e.g., a two-way Hello (HLO)packet, is received from a neighbor FC switch within a predeterminedwaiting period, the FC switch determines that the neighbor FC switchsending the two-way HLO packet has already established the adjacencyrelationship with the FC switch before the restart of the FC switch, andperforms block 102.

If the FC switch does not receive from the neighbor FC switch thetwo-way HLO packet for keeping alive the adjacency relationship withinthe predetermined waiting period (i.e., a timer for keeping alive theadjacency relationship is expired), it is determined and may beindicated that there is not a neighbor FC switch which has alreadyestablished the adjacency relationship with the FC switch before therestart of the FC switch, so that the process is terminated, theadjacency relationship between the FC switch and the neighbor FC switchis deleted, and a neighbor discovery process is re-performed with theneighbor FC switch;

if the FC switch receives from the neighbor FC switch a packet forneighbor discovery within the predetermined waiting period (i.e., beforethe expiration of the timer for keeping alive the adjacencyrelationship), i.e., the neighbor discovery initiated by the neighbor FCswitch is detected, it is indicated that the neighbor FC switch does notestablish the adjacency relationship with the FC switch before therestart of the FC switch, or, the adjacency relationship is deleted atthis time although the neighbor FC switch has established the adjacencyrelationship with the FC switch before the restart of the FC switch, sothat the process is terminated, the adjacency relationship between theFC switch and the neighbor FC switch is deleted, and the neighbordiscovery is re-performed with the neighbor FC switch.

In block 102, when the neighbor FC switch which has already establishedthe adjacency relationship with the FC switch is detected, the FC switchresponds to the neighbor FC switch with a packet for keeping alive theadjacency relationship, e.g., a two-way HLO packet.

In block 103, after responding to the neighbor FC switch the two-way HLOpacket for keeping alive the adjacency relationship, the FC switch sendsto the neighbor FC switch a LSU packet in which an initialsynchronization flag requesting state non-change is carried to requestthe neighbor FC switch to keep the adjacency relationship with the FCswitch as well as to perform LSR initial synchronization to the FCswitch.

In block 104, when a LSA packet in response to the LSU packet sent bythe FC switch and carrying the initial synchronization flag requestingstate non-change is received from the neighbor FC switch which hasalready established the adjacency relationship with the FC switch, allLSRs carried in at least one LSU packet for LSR synchronization receivedfrom the neighbor FC switch are synchronized to the FC switch, androuting calculation is triggered after the synchronization is completed.

So far, a synchronization process for the restarted FC switch iscompleted.

FIG. 2 is a flowchart illustrating a method for synchronization afterrestart of a FC switch according to another example of the presentdisclosure. As shown in FIG. 2, when the FC switch is restarted, themethod is performed by a neighbor FC switch of the restarted FC switch.The restarted FC switch has already established an adjacencyrelationship with the neighbor FC switch before the restart. The methodincludes operations as follows.

In block 201, a packet for keeping alive the adjacency relationship issent to the restarted FC switch, e.g., a two-way HLO packet.

In block 202, if a two-way HLO packet used for keeping alive theadjacency relationship and responded from the restarted FC switch isreceived within a predetermined waiting period, the adjacencyrelationship between the neighbor FC switch and the restarted FC switchis kept.

If the two-way HLO packet for keeping alive the adjacency relationshipis not received from the restarted FC switch within the predeterminedwaiting period (i.e., a timer for keeping alive the adjacencyrelationship is expired), or, the neighbor FC switch receives from therestarted FC a packet for neighbor discovery within the predeterminedwaiting period (i.e., before the expiration of the timer for keepingalive the adjacency), i.e., the neighbor discovery initiated by therestarted FC switch is detected, so that the process is terminated, theadjacency relationship between the neighbor FC switch and the restartedFC switch is deleted, and the neighbor discovery is re-performed withthe restarted FC switch.

In block 203, when a LSU packet is received from the restarted FC switchand it is detected that an initial synchronization flag requesting statenon-change is carried in the received LSU packet, the adjacencyrelationship between the neighbor FC switch and the restarted FC switchis kept, and a LSA packet is responded to the restarted FC switch.

In block 204, when the LSA packet is responded to the restarted FCswitch which sends the LSU packet carrying the initial synchronizationflag requesting state non-change, all LSRs stored in the neighbor FCswitch are sent to the restarted FC switch through at least one LSUpacket in which all of the LSRs are carried so as to synchronize withthe restarted FC switch. So far, a synchronization process for theneighbor FC switch of the restarted FC switch is completed.

As can be seen from the above description, in the methods shown in FIG.1 and FIG. 2 in accordance with examples of the present disclosure, aninitial synchronization request for keeping an adjacency relationship isimplemented through carrying an initial synchronization flag requestingstate non-change in a LSU packet. In order to carry the flag in the LSUpacket, a Flag field in the LSU packet is improved in accordance with anexample of the present disclosure.

Specifically, there is a 1-byte Flag field in the LSU packet. Only twobits in the Flag field are used, i.e., a synchronization type flag inbit 0 and a synchronization completion flag in bit 1, while theremaining 6 bits are all free, therefore, an example of the presentdisclosure configures one of the six free bits (e.g., bit 3) as a statenon-change synchronization request flag.

As such, in the Flag field of the LSU packet sent in block 103 and usedto initiate the initial synchronization request for keeping theadjacency relationship as well as the LSU packet received in block 203and used to initiate the initial synchronization request for keeping theadjacency relationship, the state non-change synchronization requestflag is configured as a valid value 1, and the synchronization type flagis configured as a type value 1 which denotes initial synchronization.

While in the Flag field of the LSU packet received in block 104 and usedto transmit LSRs normally as well as the LSU packet sent in block 204and used to transmit the LSRs normally, the state non-changesynchronization request flag is configured as an invalid value 0, andthe synchronization type flag is configured as the type value 1 whichdenotes initial synchronization.

In addition, as the LSU packet sent in block 103 is mainly used toinitiate the initial synchronization request for keeping the adjacencyrelationship rather than synchronize LSRs of the restarted FC switch tothe neighbor FC switch which has already established the adjacencyrelationship with the restarted FC switch, thus it is not necessary forthe neighbor FC switch to determine whether the restarted FC switchcompletes the LSR transmission; as a result, in the LSU packet sent inblock 103 and carrying the initial synchronization flag requesting statenon-change, the synchronization completion flag of the Flag field may bepreferably configured as the valid value 1 which denotes that the FCswitch has completed the LSR transmission; this is also applicable tothe Flag field in the LSU packet received in block 203 and carrying theinitial synchronization flag requesting state non-change.

While for the LSU packet received in block 104 and used for LSRsynchronization, and the LSU packet sent in block 204 and used for LSRsynchronization, as these LSU packets are mainly used to transmit LSRsnormally, therefore, the synchronization completion flag of the Flagfield in the above LSU packets may be configured as follows.

For block 104:

if all of LSRs stored in the neighbor FC switch which has alreadyestablished the adjacency relationship with the restarted FC switch arecarried in one LSU packet, the synchronization completion flag of theFlag field in the one LSU packet received in block 104 is configured asthe valid value 1;

if all of the LSRs stored in the neighbor FC switch which has alreadyestablished the adjacency relationship with the restarted FC switch arecarried in a plurality of LSU packets, the synchronization completionflag of the Flag field in a last LSU packet received in block 104 isconfigured as the valid value 1, and the synchronization completion flagof the Flag field in a remaining LSU packet received in block 104 isconfigured as the invalid value 0.

Similarly, for block 204:

if all of LSRs stored in the neighbor FC switch are carried in one LSUpacket, the synchronization completion flag of the Flag field in the oneLSU packet sent in block 204 is configured as the valid value 1;

if all of the LSRs stored in the neighbor FC switch are carried in aplurality of LSU packets, the synchronization completion flag of theFlag field in a last LSU packet sent in block 204 is configured as thevalid value 1, and the synchronization completion flag of the Flag fieldin a remaining LSU packet sent in block 204 is configured as the invalidvalue 0.

In order to apply the method for synchronization after restart of a FCswitch disclosed in the example of the present disclosure to a FCswitch, a neighbor state machine in the FC switch is improved inaccordance with an example of the present disclosure.

As shown in FIG. 3, the improved neighbor state machine includes Downstate, Init state, DB Exchange state, DB Wait state, DB ACK Wait stateand Full state, and Neighbor Wait state is further added in the neighborstate machine.

The neighbor state machine shown in FIG. 3 is described in detailhereinafter.

In Full state:

if a FC switch is restarted, a neighbor state machine of the FC switchis changed to Neighbor Wait state rather than changed to Down state in aconventional system, therefore, it can prevent the FC switch fromimmediately re-initiating a neighbor discovery process with a neighborFC switch after the restart of the FC switch (i.e., changing from Downstate to Init state, and sending a one-way HLO packet).

In Neighbor Wait state:

if a two-way HLO packet for keeping alive an adjacency relationship isnot received from the neighbor FC switch within a predetermined waitingperiod, i.e., a timer is expired, it is determined and may be indicatedthat there is not a neighbor FC switch which has already established theadjacency relationship with the FC switch before the restart of the FCswitch, therefore the FC switch may be rolled back to Init state tore-perform the neighbor discovery;

if a packet for neighbor discovery, e.g., a one-way HLO packet, isreceived from the neighbor FC switch within the predetermined waitingperiod, it is determined and may be indicated that the neighbor FCswitch does not establish the adjacency relationship with the FC switchbefore the restart of the FC switch, or, the adjacency relationship isdeleted at this time although the neighbor FC switch has established theadjacency relationship with the FC switch before the restart of the FCswitch, therefore the FC switch may be rolled back to Init state tore-perform the neighbor discovery;

if the two-way HLO packet for keeping alive the adjacency relationshipis received from the neighbor FC switch within the predetermined waitingperiod, it is determined and may be indicated that the neighbor FCswitch has already established the adjacency relationship with the FCswitch before the restart of the FC switch, and is in Full state,therefore the FC switch is changed to DB Exchange state.

In DB Exchange state:

if the FC switch is changed from Init state, the processing and changingapproach is the same as conventional systems, except that the foregoingstate non-change synchronization request flag is included in the Flagfield of the LSU packet and the LSA packet, and is configured as aninvalid value 0; in FIG. 3, if it is changed from Init state, a Flagfield in an interactive LSU packet for LSR synchronization may bedenoted as Flag[2:0]=0X1; the Flag field in a LSA packet sent from theneighbor FC switch and denoting that it is detected that the FC switchhas completed the transmission of all LSRs, and the Flag field in a LSUpacket sent from the neighbor FC switch and denoting that the neighborFC switch has completed the transmission of all LSRs may be denoted asFlag[2:0]=011;

if the FC switch is changed from Neighbor Wait state, a two-way HLOpacket for keeping alive the adjacency relationship is responded to theneighbor FC switch so as to begin maintenance of the adjacencyrelationship between the FC switch and the neighbor FC switch, and theneighbor state machine is kept in Full state; in addition, the FC switchtransmits to the neighbor FC switch a LSU packet in which an initialsynchronization flag requesting state non-change is carried (forexample, when the neighbor FC switch is restarted), i.e., the LSU packetfor initiating an initial synchronization request for keeping theadjacency relationship is transmitted, wherein in the Flag field of theLSU packet, the state non-change synchronization request flag isconfigured as the valid value 1, and the synchronization type flag isconfigured as the type value 1 which denotes initial synchronization;after the neighbor FC switch transmits a LSA packet in response to theLSU packet for initiating the initial synchronization request forkeeping the adjacency relationship, the FC switch is changed to DB waitstate; in FIG. 3, for a situation that the FC switch is changed fromNeighbor Wait state, the Flag field in the LSU packet for initiating theinitial synchronization request for keeping the adjacency relationship,and the Flag field in the LSA packet sent from the neighbor FC switchand in response to the LSU packet for initiating the initialsynchronization request for keeping the adjacency relationship may bedenoted as Flag[2:0]=111.

For a situation that it is changed from Neighbor Wait state to DBExchange state, a FC switch in DB Exchange state may determine that theFC switch is in an adjacency relationship with a neighbor FC switch, or,the FC switch in DB Exchange state may determine that the FC switch isin a two-way relationship with the neighbor FC switch; no matter whatcase it is, the neighbor FC switch is kept in Full state and determinesthat the neighbor FC switch is in the adjacency relationship with the FCswitch.

The above improvements are performed for a restarted FC switch.Accordingly, in the method for synchronization after restart of a FCswitch shown in FIG. 1 in accordance with the example of the presentdisclosure, block 101 is performed when the FC switch is in NeighborWait state, blocks 102 and 103 are performed when the FC switch is in DBExchange state, block 104 is performed when the FC switch is in DB Waitstate, and the FC switch is changed to Full state after block 104 iscompleted.

In addition, in Full state:

if a LSU packet is received from a neighbor FC switch and an initialsynchronization flag requesting state non-change is carried in the LSUpacket (for example, when the neighbor FC switch is restarted), i.e., aFC switch receives the LSU packet sent from the neighbor FC switch andused for initiating an initial synchronization request for keeping anadjacency relationship, and an state non-change synchronization requestflag included in a Flag field of the LSU packet is configured as a validvalue 1, and a synchronization type flag included in the Flag field ofthe LSU packet is configured as a type value 1 denoting initialsynchronization, the FC switch is kept in Full state, and transmits aLSA packet in response to the LSU packet sent from the neighbor FCswitch and used for initiating the initial synchronization request forkeeping the adjacency relationship, then synchronizes LSRs of the FCswitch to the neighbor FC switch through a LSU packet for LSRsynchronization, and receives a LSA packet sent from the neighbor FCswitch and in response to the LSU packet for LSR synchronization; assuch, it may be avoided that state rollback occurs in the FC switch whenthe neighbor FC switch is restarted; in FIG. 3, the Flag field in theLSU packet for initiating the initial request for keeping the adjacencyrelationship may be denoted as Flag[2:0]=111; the Flag field in the LSApacket in response to the LSU packet for initiating the initialsynchronization request for keeping the adjacency relationship may bedenoted as Flag[2:0]=111; the Flag field in the LSU packet forsynchronizing LSRs to the neighbor FC switch may be denoted asFlag[2:0]=0X1.

The above improvements are performed for a neighbor FC switch of arestarted FC switch. Accordingly, in the method for synchronizationafter restart of a FC switch shown in FIG. 2 in accordance with theexample of the present disclosure, blocks 201-204 are performed when theneighbor FC switch is in Full state.

The method for synchronization after restart of a FC switch inaccordance with the example of the present disclosure is furtherdescribed hereinafter with reference to an example.

FIG. 4 is a flowchart illustrating an example of a method forsynchronization after restart of a FC switch according to an example ofthe present disclosure. As shown in FIG. 4, taking switch A and switch Bwhich have established an adjacency relationship between each other asan example, switches A and B may be FC switches, or may be Fiber Channelover Ethernet (FCoE) switches. The flowchart includes operations asfollows.

In block 400, switch A is restarted, and is changed from Full state toNeighbor Wait state; switch B is still in Full state.

In block 401, in order to maintain the adjacency relationship betweenswitch A and switch B, switch B which is in Full state sends to switch Aa two-way HLO packet for keeping alive the adjacency relationship;accordingly, switch A which is in Neighbor Wait state is able to receivethe two-way HLO packet sent by switch B, and thus is able to determinethat switch B has already established the adjacency relationship withswitch A before the restart of switch A, and is changed to DB Exchangestate.

In block 402, in order to avoid that state rollback occurs in switch B,switch A which is in DB Exchange state sends to switch B the two-way HLOpacket for keeping alive the adjacency relationship; accordingly, switchB is able to receive the two-way HLO packet sent by switch A, and thusis able to continue keeping the adjacency relationship with switch A,and is still in Full state.

In block 403, switch A which is in DB Exchange state sends to switch B aLSU packet with Flag[2:0]=111 to request switch B to keep the adjacencyrelationship with switch A and perform LSR initial synchronization toswitch A; accordingly, after receiving the LSU packet with Flag[2:0]=111sent by switch A, switch B is still in Full state.

In block 404, in order to respond to the LSU packet sent by switch A andused for requesting switch B to keep the adjacency relationship withswitch A and performing LSR initial synchronization to switch A, switchB which is in Full state sends to switch A a LSA packet withFlag[2:0]=111; accordingly, switch A is able to receive the LSA packetwith Flag[2:0]=111 sent by switch B, and detect that switch B is aboutto synchronize LSRs to switch A; switch A is changed to DB Wait state.

In blocks 405-406, switch B which is in Full state sends to switch A aLSU packet with Flag[2:0]=0X1 in which all of LSRs stored in switch Bare carried; accordingly, switch A which is in DB Wait state sends toswitch B a LSA packet with Flag[2:0]=0X1 in response to each LSU packetcarrying the LSR of switch B. The above operations are performedrepeatedly until all LSRs in a LSDB of switch B are synchronized toswitch A, and switch A is changed to Full state after thesynchronization is completed.

In block 407, switch A which is in Full state updates locally storedLSRs to the synchronized LSRs received by switch A.

In block 408, switch A which is in Full state calculates routing ofswitch A.

In block 409, switch A which is in Full state issues the routingcalculated by switch A.

So far, a synchronization recovery process after the restart of switch Ais completed. After the process is completed, switch A is able to startrouting forwarding; moreover, switch B is able to continue implementingthe routing forwarding during the synchronization process.

The above is the description about the method for synchronization afterrestart of a FC switch in accordance with the example of the presentdisclosure. Based on the same principles as the method, an example ofthe present disclosure provides an apparatus for synchronization afterrestart of a FC switch.

An apparatus for synchronization after restart of a FC switch inaccordance with an example of the present disclosure, which isapplicable to the restarted FC switch, includes:

a neighbor waiting module, adapted to determine, when the FC switch isrestarted and when a packet for keeping alive an adjacency relationship,e.g., a two-way HLO packet, is received from a neighbor FC switch withina predetermined waiting period, that the neighbor FC switch sending thetwo-way HLO packet has already established the adjacency relationshipwith the FC switch before the restart of the FC switch.

In practice, if the neighbor waiting module does not receive from theneighbor FC switch the two-way HLO packet for keeping alive theadjacency relationship within the predetermined waiting period (i.e., atimer for keeping alive the adjacency relationship is expired), it isdetermined and indicated that there is not a neighbor FC switch whichhas already established the adjacency relationship with the FC switchbefore the restart of the FC switch, so that the process of theapparatus is terminated, the adjacency relationship between the FCswitch and the neighbor FC switch is deleted and a neighbor discoveryprocess is re-performed with the neighbor FC switch by another module ofthe FC switch;

if the neighbor waiting module receives from the neighbor FC switch apacket for neighbor discovery within the predetermined waiting period(i.e., before the expiration of the timer for keeping alive theadjacency relationship), i.e., the neighbor discovery initiated by theneighbor FC switch is detected, it is determined and may be indicatedthat the neighbor FC switch does not establish the adjacencyrelationship with the FC switch before the restart of the FC switch, or,the adjacency relationship is deleted at this time although the neighborFC switch has established the adjacency relationship with the FC switchbefore the restart of the FC switch, so that the process of theapparatus is terminated, the adjacency relationship between the FCswitch and the neighbor FC switch is deleted and the neighbor discoveryis re-performed with the neighbor FC switch through the other module ofthe FC switch.

A first neighbor maintaining module, adapted to respond to the neighborFC switch a packet for keeping alive the adjacency relationship, e.g.,the two-way HLO packet when the neighbor FC switch which has alreadyestablished the adjacency relationship with the FC switch is detected.

A synchronization requesting module, adapted to send to the neighbor FCswitch, after responding to the neighbor FC switch the two-way HLOpacket for keeping alive the adjacency relationship, a LSU packet inwhich an initial synchronization flag requesting state non-change iscarried to request the neighbor FC switch to keep the adjacencyrelationship with the FC switch as well as to perform LSR initialsynchronization to the FC switch.

A synchronization receiving module, adapted to synchronize to the FCswitch all LSRs carried in at least one LSU packet for LSRsynchronization received from the neighbor FC switch when a LSA packetin response to the LSU packet sent by the synchronization requestingmodule of the apparatus and carrying the initial synchronization flagrequesting state non-change is received from the neighbor FC switchwhich has already established the adjacency relationship with the FCswitch; and trigger routing calculation after the synchronization iscompleted.

The above modules may be implemented by software (e.g. machine readableinstructions stored in a memory and executable by a processor), hardware(e.g., the processor of an application specific integrated circuit(ASIC)), or a combination thereof.

An apparatus for synchronization after restart of a FC switch inaccordance with another example of the present disclosure is applicableto a neighbor FC switch of the restarted FC switch, wherein therestarted FC switch has already established an adjacency relationshipwith the neighbor FC switch before the restart. The apparatus includes:

a second neighbor maintaining module, adapted to send a packet forkeeping alive the adjacency relationship, e.g., a two-way HLO packet, tothe restarted FC switch.

A local maintaining module, adapted to keep the adjacency relationshipbetween the neighbor FC switch and the restarted FC switch when atwo-way HLO packet for keeping alive the adjacency relationship isreceived from the restarted FC switch within a predetermined waitingperiod.

In practice, if the local maintaining module does not receive from therestarted FC switch the two-way HLO packet for keeping alive theadjacency relationship within the predetermined waiting period (i.e., atimer for keeping alive the adjacency relationship is expired), or,receives from the restarted FC a packet for neighbor discovery withinthe predetermined waiting period (i.e., before the expiration of thetimer for keeping alive the adjacency), i.e., the neighbor discoveryinitiated by the restarted FC switch is detected, so that the process ofthe apparatus is terminated, the adjacency relationship between theneighbor FC switch and the restarted FC switch is deleted and theneighbor discovery is re-performed with the restarted FC switch byanother module of the neighbor FC switch.

A synchronization responding module, adapted to keep, when a LSU packetis received from the restarted FC switch and it is detected that aninitial synchronization flag requesting state non-change is carried inthe received LSU packet, the adjacency relationship between the neighborFC switch and the restarted FC switch, and respond to the restarted FCswitch a LSA packet.

A synchronization sending module, adapted to send to the restarted FCswitch, after the synchronization responding module responds the LSApacket to the restarted FC switch which sends the LSU packet carryingthe initial synchronization flag requesting state non-change, all ofLSRs stored in the neighbor FC switch through at least one LSU packet inwhich the LSRs are carried so as to synchronize with the restarted FCswitch.

In addition, a Flag field in the above LSU packet and/or the LSA packetis the same as the method example described above, and is not repeatedherein.

The above modules may be implemented by software (e.g. machine readableinstructions stored in a memory and executable by a processor), hardware(e.g., the processor of an ASIC), or a combination thereof.

FIG. 5 is a schematic diagram illustrating a hardware structureaccording to an example of the present disclosure. As shown in FIG. 5,the hardware structure at least includes a master control board and aninterface board, and may also include a backup master control board(shown with a dashed line in FIG. 5). The master control board isconfigured with a Central Processing Unit (CPU), which is used toimplement various processes of the master control board, and implement aprotocol layer for implementing routing calculation; the interface boardis configured with a processor, a forwarding chip and a port, whereinthe processor is used to implement various processes of the interfaceboard, the forwarding chip is used to implement various processes of ahardware layer, and the port is used to implement interaction between alocal and a neighbor FC switch.

In the hardware structure shown in FIG. 5, the CPU of the master controlboard may perform the method for synchronization after restart of a FCswitch in accordance with the example of the present disclosure, or,include the apparatus for synchronization after restart of a FC switchin accordance with the example of the present disclosure.

FIG. 6A is a schematic diagram illustrating a hardware structure of anapparatus for synchronization after restart of a FC switch according toan example of the present disclosure. The apparatus is applicable to therestarted FC switch, and includes processor 601 and storage 602,wherein,

storage 602 is adapted to store machine readable instructions; and

processor 601 is adapted to execute the machine readable instructions toperform operations including:

when the apparatus is restarted and when a packet for keeping alive anadjacency relationship, e.g., a two-way HLO packet, is received within apredetermined waiting period, determining that a neighbor FC switchsending the two-way HLO packet has already established the adjacencyrelationship with the apparatus before the restart of the apparatus;

when the neighbor FC switch which has already established the adjacencyrelationship with the apparatus is detected, responding to the neighborFC switch a packet for keeping alive the adjacency relationship, e.g.,the two-way HLO packet;

after responding to the neighbor FC switch the two-way HLO packet forkeeping alive the adjacency relationship, sending to the neighbor FCswitch a LSU packet in which an initial synchronization flag requestingstate non-change is carried to request the neighbor FC switch to keepthe adjacency relationship with the apparatus as well as to perform LSRinitial synchronization to the apparatus;

when a LSA packet in response to the LSU packet sent by the apparatusand carrying the initial synchronization flag requesting statenon-change is received from the neighbor FC switch which has alreadyestablished the adjacency relationship with the apparatus, synchronizingall LSRs carried in at least one LSU packet for LSR synchronizationreceived from the neighbor FC switch to the apparatus; and triggering arouting calculation after the synchronization is completed.

Furthermore, a Flag field is included in the LSU packet, wherein theFlag field includes a state non-change synchronization request flag anda synchronization type flag. In the Flag field of the LSU packet sent tothe neighbor FC switch and carrying the initial synchronization flagrequesting state non-change, the state non-change synchronizationrequest flag may be configured as a valid value, e.g., 1; and thesynchronization type flag may be configured as a type value denotinginitial synchronization, e.g., 1;

in the Flag field of the at least one LSU packet received from theneighbor FC switch and used for LSR synchronization, the statenon-change synchronization request flag may be configured as an invalidvalue, e.g., 0; and the synchronization type flag may be configured asthe type value denoting initial synchronization.

The Flag field further includes a synchronization completion flag,wherein,

in the Flag field of the LSU packet sent to the neighbor FC switch andcarrying the initial synchronization flag requesting state non-change,the synchronization completion flag may be configured as a valid value,e.g., 1;

if all of the LSRs stored in the neighbor FC switch are carried in oneLSU packet used for LSR synchronization, the synchronization completionflag of the Flag field in the one LSU packet used for LSRsynchronization and received from the neighbor FC switch may beconfigured as the valid value;

if all of the LSRs stored in the neighbor FC switch are carried in aplurality of LSU packets used for LSR synchronization, thesynchronization completion flag of the Flag field in a last LSU packetused for LSR synchronization and received from the neighbor FC switchmay be configured as the valid value, and the synchronization completionflag of the Flag field in a remaining LSU packet used for LSRsynchronization and received from the neighbor FC switch may beconfigured as the invalid value, e.g., 0.

As can be seen from the above description, when the machine readableinstruction stored in storage 602 are executed by processor 601,functions of the foregoing neighbor waiting module, the first neighbormaintaining module, the synchronization requesting module and thesynchronization receiving module are implemented. Therefore, thehardware structure of the apparatus for synchronization after restart ofa FC switch shown in FIG. 6A may also be shown in FIG. 6B, wherein theapparatus shown in FIG. 6B further includes I/O port 603.

FIG. 7A is a schematic diagram illustrating a hardware structure ofanother apparatus for synchronization after restart of a FC switchaccording to an example of the present disclosure. The apparatus isapplicable to a neighbor FC switch of the restarted FC switch, whereinthe restarted FC switch has already established an adjacencyrelationship with the neighbor FC switch before the restart. Theapparatus includes processor 701 and storage 702, wherein,

storage 702 is adapted to store machine readable instructions; and

processor 701 is adapted to execute the machine readable instructions toperform operations including:

sending to the restarted FC switch a packet for keeping alive theadjacency relationship, e.g., a two-way HLO packet;

if a two-way HLO packet for keeping alive the adjacency relationship isreceived from the restarted FC switch within a predetermined waitingperiod, keeping the adjacency relationship between the apparatus and therestarted FC switch;

when a LSU packet is received from the restarted FC switch and it isdetected that an initial synchronization flag requesting statenon-change is carried in the received LSU packet, keeping the adjacencyrelationship between the apparatus and the restarted FC switch, andresponding to the restarted FC switch a LSA packet;

after the LSA packet is responded to the restarted FC switch which sendsthe LSU packet carrying the initial synchronization flag requestingstate non-change, sending to the restarted FC switch all of LSRs storedin the apparatus through at least one LSU packet in which all of theLSRs are carried so as to synchronize with the restarted FC switch.

Furthermore, a Flag field is included in the LSU packet, wherein theFlag field includes a state non-change synchronization request flag anda synchronization type flag. In the Flag field of the LSU packetreceived from the neighbor FC switch and carrying the initialsynchronization flag requesting state non-change, the state non-changesynchronization request flag may be configured as a valid value, e.g.,1; and the synchronization type flag may be configured as a type valuedenoting initial synchronization, e.g., 1;

in the Flag field of the at least one LSU packet sent to the neighbor FCswitch and used for LSR synchronization, the state non-changesynchronization request flag may be configured as an invalid value,e.g., 0; and the synchronization type flag may be configured as the typevalue denoting initial synchronization.

The Flag field further includes a synchronization completion flag,wherein,

in the Flag field of the LSU packet received from the neighbor FC switchand carrying the initial synchronization flag requesting statenon-change, the synchronization completion flag may be configured as avalid value, e.g., 1;

if all of the LSRs stored in the apparatus are carried in one LSU packetused for LSR synchronization, the synchronization completion flag of theFlag field in the one LSU packet used for LSR synchronization and sentto the neighbor FC switch may be configured as the valid value;

if all of the LSRs stored in the apparatus are carried in a plurality ofLSU packets used for LSR synchronization, the synchronization completionflag of the Flag field in a last LSU packet used for LSR synchronizationand sent to the neighbor FC switch may be configured as the valid value,and the synchronization completion flag of the Flag field in a remainingLSU packet used for LSR synchronization and sent to the neighbor FCswitch may be configured as an invalid value, e.g., 0.

As can be seen from the above description, when the machine readableinstruction stored in storage 702 are executed by processor 701,functions of the foregoing second neighbor maintaining module, the localmaintaining module, the synchronization responding module and thesynchronization sending module are implemented. Therefore, the hardwarestructure of the apparatus for synchronization after restart of a FCswitch shown in FIG. 7A may be also shown in FIG. 7B, wherein theapparatus shown in FIG. 7B further includes I/O port 703.

As can be seen from the above technical solution, in the examples of thepresent disclosure, when a FC switch which is restarted detects that aneighbor FC switch has already established an adjacency relationshipwith the restarted FC switch, the adjacency relationship between therestarted FC switch and the neighbor FC switch is maintainedimmediately, and the neighbor FC switch is requested to perform LSRinitial synchronization to the restarted FC switch under a circumstancethat the adjacency relationship is kept. As such, state rollbackoccurring in the neighbor FC switch can be avoided and deletion of theadjacency relationship between the neighbor FC switch and the restartedFC switch can be avoided. Therefore, the routing from another FC switchin a FC network to the restarted FC switch through the neighbor switchFC being deleted can be avoided, so that the routing from the other FCswitch in the FC network to the restarted FC switch is not changedbefore and after the restart of the restarted FC switch;

in addition, the restarted FC switch is capable of detecting the sameLSRs as ones before the restart of the restarted FC switch through theLSR initial synchronization, therefore routing from the restarted FCswitch to the other FC switch in the FC network which is re-calculatedby the restarted FC switch is the same as one before the restart of therestarted FC switch; moreover, the restarted FC switch triggers routingcalculation after the initial synchronization is completed rather thanperforms the routing calculation during the process of the initialsynchronization. Therefore, frequent changing of the routing from therestarted FC switch to the other FC switch in the FC network which isre-calculated by the restarted FC switch following the process of theinitial synchronization can be avoided. Therefore, a change in therouting in the FC network due to the restart of the FC switch can beavoided.

The above examples can be implemented by hardware, software or firmwareor a combination thereof. For example the various methods, processes andfunctional units described herein may be implemented by a processor (theterm processor is to be interpreted broadly to include a CPU, processingunit, ASIC, logic unit, or programmable gate array etc.). The processes,methods and functional units may all be performed by a single processoror split between several processors; reference in this disclosure or theclaims to a ‘processor’ should thus be interpreted to mean ‘one or moreprocessors’. The processes, methods and functional units be implementedas machine readable instructions executable by one or more processors,hardware logic circuitry of the one or more processors or a combinationthereof. Further the teachings herein may be implemented in the form ofa software product. The computer software product is stored in anon-transitory storage medium and comprises a plurality of instructionsfor making a computer apparatus (which can be a personal computer, aserver or a network apparatus such as a router, switch, access pointetc.) implement the method recited in the examples of the presentdisclosure.

The figures are only illustrations of examples, wherein the units orprocedure shown in the figures are not necessarily essential forimplementing the present disclosure. The units in the aforesaid examplescan be combined into one unit or further divided into a plurality ofsub-units.

The above are just several examples of the present disclosure, and arenot used for limiting the protection scope of the present disclosure.Any modifications, equivalents, improvements, etc., made under theprinciple of the present disclosure should be included in the protectionscope of the present disclosure.

What is claimed is:
 1. A method for synchronization after restart of a Fiber Channel (FC) switch, wherein the method is applied at a first FC switch which is restarted; the method comprising: when the first FC switch is restarted and a first packet for keeping alive an adjacency relationship is received from a second FC switch within a predetermined waiting period, determining that the second FC switch which sends the first packet has already established the adjacency relationship with the first FC switch before the restart of the first FC switch; responding to the second FC switch a second packet for keeping alive the adjacency relationship; requesting the second FC switch to perform Link State Record (LSR) initial synchronization to the first FC switch under a circumstance that the adjacency relationship is kept; and triggering routing calculation after the LSR initial synchronization is completed.
 2. The method of claim 1, wherein the requesting the second FC switch to perform LSR initial synchronization to the first FC switch under a circumstance that the adjacency relationship is kept comprises: sending to the second FC switch a Link State Update (LSU) packet in which an initial synchronization flag requesting state non-change is carried to request the second FC switch to keep the adjacency relationship with the first FC switch and to perform the LSR initial synchronization to the first FC switch; and when a Link State Acknowledgement (LSA) packet in response to the LSU packet sent by the first FC switch and carrying the initial synchronization flag requesting state non-change is received from the second FC switch, synchronizing all of LSRs carried in at least one LSU packet for LSR synchronization received from the second FC switch to the first FC switch.
 3. The method of claim 2, wherein the LSU packet comprises a Flag field including a state non-change synchronization request flag and a synchronization type flag, wherein, in the Flag field of the LSU packet sent to the second FC switch and carrying the initial synchronization flag requesting state non-change, the state non-change synchronization request flag is configured as a valid value, and the synchronization type flag is configured as a type value denoting initial synchronization; and in the Flag field of the at least one LSU packet received from the second FC switch and used for LSR synchronization, the state non-change synchronization request flag is configured as an invalid value, and the synchronization type flag is configured as the type value denoting initial synchronization.
 4. The method of claim 3, wherein the Flag field further comprises a synchronization completion flag, wherein, in the Flag field of the LSU packet sent to the second FC switch and carrying the initial synchronization flag requesting state non-change, the synchronization completion flag is configured as the valid value; if all of the LSRs of the second FC switch are carried in one LSU packet used for LSR synchronization, the synchronization completion flag of the Flag field in the one LSU packet used for LSR synchronization and received from the second FC switch is configured as the valid value; and if all of the LSRs of the second FC switch are carried in a plurality of LSU packets used for LSR synchronization, the synchronization completion flag of the Flag field in a last LSU packet used for LSR synchronization and received from the second FC switch is configured as the valid value, and the synchronization completion flag of the Flag field in a remaining LSU packet used for LSR synchronization and received from the second FC switch is configured as the invalid value.
 5. A method for synchronization after restart of a Fiber Channel (FC) switch, wherein the method is applied at a neighbor FC switch of a first FC switch which is restarted, and the first FC switch has already established an adjacency relationship with the neighbor FC switch before the restart of the first FC switch; the method comprising: sending to the first FC switch a first packet for keeping alive the adjacency relationship after the first FC switch is restarted; if a second packet for keeping alive the adjacency relationship is received from the first FC switch within a predetermined waiting period, keeping the adjacency relationship with the first FC switch; and performing Link State Record (LSR) initial synchronization to the first FC switch under a circumstance that the adjacency relationship is kept.
 6. The method of claim 5, wherein the performing LSR initial synchronization to the first FC switch under a circumstance that the adjacency relationship is kept comprises: when a Link State Update (LSU) packet is received from the first FC switch and it is detected that an initial synchronization flag requesting state non-change is carried in the received LSU packet, keeping the adjacency relationship with the first FC switch, and responding to the first FC switch a Link State Acknowledgement (LSA) packet; and sending to the first FC switch all of LSRs stored in the neighbor FC switch through at least one LSU packet in which all of the LSRs are carried so as to synchronize with the first FC switch.
 7. The method of claim 6, wherein the LSU packet comprises a Flag field including a state non-change synchronization request flag and a synchronization type flag, wherein, in the Flag field of the LSU packet received from the first FC switch and carrying the initial synchronization flag requesting state non-change, the state non-change synchronization request flag is configured as a valid value, and the synchronization type flag is configured as a type value denoting initial synchronization; and in the Flag field of the at least one LSU packet sent to the first FC switch and used for LSR synchronization, the state non-change synchronization request flag is configured as an invalid value, and the synchronization type flag is configured as the type value denoting initial synchronization.
 8. The method of claim 7, wherein the Flag field further comprises a synchronization completion flag, wherein, in the Flag field of the LSU packet received from the first FC switch and carrying the initial synchronization flag requesting state non-change, the synchronization completion flag is configured as the valid value; if all of the LSRs stored in the neighbor FC switch are carried in one LSU packet used for LSR synchronization, the synchronization completion flag of the Flag field in the one LSU packet used for LSR synchronization and sent to the first FC switch is configured as the valid value; and if all of the LSRs stored in the neighbor FC switch are carried in a plurality of LSU packets used for LSR synchronization, the synchronization completion flag of the Flag field in a last LSU packet used for LSR synchronization and sent to the first FC switch is configured as the valid value, and the synchronization completion flag of the Flag field in a remaining LSU packet used for LSR synchronization and sent to the first FC switch is configured as the invalid value.
 9. A first Fiber Channel (FC) switch, comprising a processor and a storage, wherein, the storage is to store machine readable instructions; and the processor is to execute the machine readable instructions to perform operations including: when the first FC switch is restarted and a first packet for keeping alive an adjacency relationship is received from a second FC switch within a predetermined waiting period, determining that the second FC switch which sends the first packet has already established the adjacency relationship with the first FC switch before the restart of the first FC switch; responding to the second FC switch a second packet for keeping alive the adjacency relationship; requesting the second FC switch to perform Link State Record (LSR) initial synchronization to the first FC switch under a circumstance that the adjacency relationship is kept; and triggering routing calculation after the LSR initial synchronization is completed.
 10. The first FC switch of claim 9, wherein the processor is further to execute the machine readable instructions to perform operations including: sending to the second FC switch a Link State Update (LSU) packet in which an initial synchronization flag requesting state non-change is carried to request the second FC switch to keep the adjacency relationship with the first FC switch and to perform the LSR initial synchronization to the first FC switch; and when a Link State Acknowledgement (LSA) packet in response to the LSU packet sent by the first FC switch and carrying the initial synchronization flag requesting state non-change is received from the second FC switch, synchronizing all of LSRs carried in at least one LSU packet for LSR synchronization received from the second FC switch to the first FC switch.
 11. The first FC switch of claim 10, wherein the LSU packet comprises a Flag field including a state non-change synchronization request flag and a synchronization type flag, wherein, in the Flag field of the LSU packet sent to the second FC switch and carrying the initial synchronization flag requesting state non-change, the state non-change synchronization request flag is configured as a valid value, and the synchronization type flag is configured as a type value denoting initial synchronization; and in the Flag field of the at least one LSU packet received from the second FC switch and used for LSR synchronization, the state non-change synchronization request flag is configured as an invalid value, and the synchronization type flag is configured as the type value denoting initial synchronization.
 12. The first FC switch of claim 11, wherein the Flag field further comprises a synchronization completion flag, wherein, in the Flag field of the LSU packet sent to the second FC switch and carrying the initial synchronization flag requesting state non-change, the synchronization completion flag is configured as the valid value; if all of the LSRs of the second FC switch are carried in one LSU packet used for LSR synchronization, the synchronization completion flag of the Flag field in the one LSU packet used for LSR synchronization and received from the second FC switch is configured as the valid value; and if all of the LSRs of the second FC switch are carried in a plurality of LSU packets used for LSR synchronization, the synchronization completion flag of the Flag field in a last LSU packet used for LSR synchronization and received from the second FC switch is configured as the valid value, and the synchronization completion flag of the Flag field in a remaining LSU packet used for LSR synchronization and received from the second FC switch is configured as the invalid value.
 13. A neighbor Fiber Channel (FC) switch, wherein the neighbor FC switch is a neighbor of a first FC switch which is restarted, and the first FC switch has already established an adjacency relationship with the neighbor FC switch before the restart of the first FC switch, the neighbor FC switch comprising a processor and a storage, wherein, the storage is to store machine readable instructions; and the processor is to execute the machine readable instructions to perform operations including: sending to the first FC switch a first packet for keeping alive the adjacency relationship after the first FC switch is restarted; if a second packet for keeping alive the adjacency relationship is received from the first FC switch within a predetermined waiting period, keeping the adjacency relationship with the first FC switch; and performing Link State Record (LSR) initial synchronization to the first FC switch under a circumstance that the adjacency relationship is kept.
 14. The neighbor FC switch of claim 13, wherein the processor is further to execute the machine readable instructions to perform operations including: when a Link State Update (LSU) packet is received from the first FC switch and it is detected that an initial synchronization flag requesting state non-change is carried in the received LSU packet, keeping the adjacency relationship with the first FC switch, and responding to the first FC switch a Link State Acknowledgement (LSA) packet; and sending to the first FC switch all of locally stored LSRs through at least one LSU packet in which all of the LSRs are carried so as to synchronize with the first FC switch.
 15. The neighbor FC switch of claim 14, wherein the LSU packet comprises a Flag field including a state non-change synchronization request flag and a synchronization type flag, wherein, in the Flag field of the LSU packet received from the first FC switch and carrying the initial synchronization flag requesting state non-change, the state non-change synchronization request flag is configured as a valid value, and the synchronization type flag is configured as a type value denoting initial synchronization; in the Flag field of the at least one LSU packet sent to the first FC switch and used for LSR synchronization, the state non-change synchronization request flag is configured as an invalid value, and the synchronization type flag is configured as the type value denoting initial synchronization; wherein the Flag field further comprises a synchronization completion flag, wherein, in the Flag field of the LSU packet received from the first FC switch and carrying the initial synchronization flag requesting state non-change, the synchronization completion flag is configured as the valid value; if all of the locally stored LSRs are carried in one LSU packet used for LSR synchronization, the synchronization completion flag of the Flag field in the one LSU packet used for LSR synchronization and sent to the first FC switch is configured as the valid value; and if all of the locally stored LSRs are carried in a plurality of LSU packets used for LSR synchronization, the synchronization completion flag of the Flag field in a last LSU packet used for LSR synchronization and sent to the first FC switch is configured as the valid value, and the synchronization completion flag of the Flag field in a remaining LSU packet used for LSR synchronization and sent to the first FC switch is configured as the invalid value. 